The present invention relates to mechanisms for altering the actuation of valves in internal combustion engines; more particularly, to finger follower type rocker arms having means for changing between high and low or no valve lifts; and most particularly, to a two-step finger follower type rocker arm having a slider member disposed in a passage in a finger follower body for sliding motion in the direction of lift between high and low positions and having a locking pin operative in an orthogonal bore in the finger follower body for latching and unlatching the slider member and the finger follower body to shift between high lift and low lift modes.
Variable valve activation (VVA) mechanisms for internal combustion engines are well known. It is known to be desirable to lower the lift, or even to provide no lift at all, of one or more valves of a multiple-cylinder engine, especially intake valves, during periods of light engine load. Such deactivation can substantially improve fuel efficiency.
Various approaches have been disclosed for changing the lift of valves in a running engine. One known approach is to provide an intermediary cam follower arrangement which is rotatable about the engine camshaft and is capable of changing both the valve lift and timing, the cam shaft typically having both high-lift and low-lift lobes for each such valve. Such an arrangement can be complicated and costly to manufacture and difficult to install onto a camshaft during engine assembly.
Another known approach is to provide a deactivation mechanism in the hydraulic lash adjuster (HLA) upon which a cam follower rocker arm pivots. Such an arrangement is advantageous in that it can provide variable lift from a single cam lobe by making the HLA either competent or incompetent to transfer the motion of the cam eccentric to the valve stem. A shortcoming of providing deactivation at the HLA end of a rocker arm is that, because the cam lobe actuates the rocker near its longitudinal center point, the variation in lift produced at the valve-actuating end can be only about one-half of the extent of travel of the HLA deactivation mechanism.
Still another known approach is to provide a deactivation mechanism in the valve-actuating end of a rocker arm cam follower (opposite from the HLA pivot end) which locks and unlocks the valve actuator portion from the follower body. Unlike the HLA deactivation approach, this approach typically requires both high-lift and low-lift cam lobes to provide variable lift.
It is a principal object of the present invention to provide a simplified variable valve lift apparatus.
It is a further object of the invention to provide an increased range of motion between a high lift and a low lift position of an engine valve.
Briefly described, a two-step finger follower rocker arm assembly in accordance with the invention includes an elongate, rigid follower body having a socket at a first end for engaging a conventional hydraulic lash adjuster as a pivot means, and having an arcuate pad at a second and opposite end for engaging a valve stem or lifter means. A passage through the follower body in the direction of actuation by an engine cam lobe is slidingly receivable of a reciprocating slider member for variably engaging a central cam lobe, preferably a high-lift lobe. A transverse bore in the follower body intersects the passage. A slot is provided in the slider member, and an elongate shaft extends through the bore in the body and through the slot in the slider member such that the maximum length of travel of the slider member in the passage is limited by the length of the clearance between the shaft and the slot. Outboard of the follower body, the shaft is provided on either side of the body with first and second lateral roller followers, preferably rotatably mounted in bearings on the shaft, for variably engaging first and second lateral cam lobes, preferably low-lift lobes, flanking the central cam lobe. A lost-motion spring urges the slider member into contact with the central lobe, and the hydraulic lash adjuster urges the lateral rollers into contact with the lateral lobes. A transverse locking pin can selectively engage and lock the slider member to the follower body such that the follower follows the motion of the central cam lobe. When the locking pin is disengaged from the slider member, the member slides within the passage formed in the follower body, allowing the lateral rollers to engage and follow the lateral lobes. Preferably, the central lobe is a high-lift lobe and the lateral lobes are low-lift lobes. Preferably, the locking pin is provided as a pre-assembled cartridge unit. To reduce undesirable torque and resulting wear on the slider in the passage, caused by sliding action of the slider against the central cam lobe, a wall of the passage preferably is extended to increase the resistive torque moment of the slider in the passage.